The present invention relates to a drilling and thread forming rotary threaded fastener or screw, and more particularly to a drilling and thread forming screw which causes the chips formed thereby to break into small discrete pieces.
In U.S. Pat. No. 3,395,603 E. J. Skierski there is shown a drilling and thread forming screw comprising a trailing threaded shank and a pilot end designed to drill through a workpiece of material such as sheet metal. Fasteners of this type have generally met with acceptance in the automotive, building, and appliance fields due to the simplicity of assembly or fabrication as a consequence of their use which results in a savings in both time and money in the assembly operation.
One of the problems which is often confronted in the utilization of fasteners of this type, is the creation of a metal chip which takes the form of a continuous thread of metal formed during the drilling operation of the fastener. These chips may become lodged under the head of the fastener, and are subject to rusting, resulting in an unsightly appearance and an undesirable projection on the surface fastened. It has therefore, been suggested that means be provided on the pilot end of a drilling screw to cause breakage of the metal chip and eliminate the creation of a continuous ribbon-like chip such as may be formed by application of the screw in materials such as sheet metal. Such an arrangement is shown in U.S. Pat. No. 3,786,713 to Henry A. Sygnator.
The present invention, however, takes advantage of the fact that the metal chip in most instances, takes the form of a continuous thread of material due to the fact that any bending of the chip is on a large radius, and that the chip when bent into a tight radius would, in most instances, break into small increments.
It is therefore an object of the present invention to provide a drilling and thread forming screw which does not create a continuous ribbon-like strip of material during application.
Another object of the invention is to provide a drilling and thread forming screw which is capable of breaking a chip of material formed thereby into small discrete particles.
A further object of the invention is to provide a drilling and thread forming screw having a chip breaker formed on the pilot end thereof which is both simple and economical to manufacture.